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Grilli F.,Karlsruhe Institute of Technology | Chervyakov A.,Institute for Advanced Sustainability Studies | Zermeno V.,Karlsruhe Institute of Technology | Marian A.,Institute for Advanced Sustainability Studies | And 3 more authors.
Physica C: Superconductivity and its Applications | Year: 2014

Cables made of MgB2 superconductors are currently explored as a viable solution for transporting high electrical power in the AC regime. In order to be competitive against the DC solution, the cables need to have an acceptable level of AC losses. In this contribution, we discuss the main aspects relevant for designing a cable with a sufficiently low AC loss level. To this end, we perform finite-element-method (FEM) simulations to determine the current and field distributions and calculate the AC losses of such cable configuration. For current capacities of 2-5 kA (peak), power cables are assembled from a relatively small number of MgB2 strands. The performance of such cables strongly depends on the current and field distributions, which are in turn influenced by the number and the arrangement of the superconducting components and also by the magnetic properties of supporting materials. Numerical simulations can help to test different cable configurations and provide important insights for optimizing the cable's design. The numerical model includes the field dependence of the superconductor's critical current density Jc(B) as well as the non-linear properties of magnetic materials. © 2014 Published by Elsevier B.V.

Vignolo M.,CNR Institute of Neuroscience | Bovone G.,University of Genoa | Matera D.,CNR Institute of Neuroscience | Nardelli D.,Columbus Superconductors | And 3 more authors.
Chemical Engineering Journal | Year: 2014

In the present paper a new process for large scale production of nano-sized boron is reported. The process can be summarized in several steps: boron oxide solubilization in hot water, cryogenic freezing of liquid phase, freezing-drying process, magnesiothermic reduction of boron oxide, boron purification. Each step is described in order to show the innovations and then the purified boron has been employed to synthesize the superconducting MgB2 powder. It is worth to note that for the first time the same MgB2 precursors were used to prepare the superconducting phase following four different techniques and the results directly compared. So several MgB2 conductors were prepared applying different techniques, ex-situ, in-situ, via MgB4 and RLI, and then their superconducting properties investigated. Furthermore morphology, grain size and purity of B and MgB2 powder were analyzed by SEM analysis and X-ray diffraction technique. © 2014 Elsevier B.V.

Kulich M.,University of Geneva | Flukiger R.L.,University of Geneva | Senatore C.,University of Geneva | Tropeano M.,Columbus Superconductors | Piccardo R.,Columbus Superconductors
Superconductor Science and Technology | Year: 2013

A substantially different behaviour was observed between MgB2 wires produced either by in situ or ex situ processing after applying the recently developed technique of cold high pressure densification (or CHPD). In contrast to in situ wires, where densification at 1.5 GPa on binary and ternary alloyed in situ MgB2 wires causes an enhancement of mass density and a strong enhancement of Jc, ex situ wires up to 2 GPa show only a negligible enhancement of the MgB2 mass density, while a considerable enhancement of Jc is still observed. In both cases, this reflects an enhancement of grain connectivity, however in ex situ wires, the enhancement of Jc is connected to the partial disruption of the oxide layer around each MgB2 powder particle, in contrast to the enhancement of J c in situ wires, which is correlated to a smaller void fraction and a larger contact area between neighbouring grains. It is well known that J c of ex situ wires decreases after longer exposition times when exposed to air prior to annealing; after several months Jc falls to values ≤50% of the original value. After cold pressing, we have found that Jc of the same wire exceeded the original values, even after exposing the unreacted wire for >1 year to air. A lower electrical resistivity is measured on pressed ex situ MgB2 wires, which confirms the improvement of grain connectivity due to the breakage of the oxide layers. Thus, the application of high pressure at room temperature allows us to recover the values of Jc for ex situ wires even after they have been degraded either by low quality MgB2 precursors or by prolonged ageing of the already formed wire prior to the final heat treatment. The limits of the J c enhancement in ex situ wires are discussed. © 2013 IOP Publishing Ltd.

Nardelli D.,Columbus Superconductors | Matera D.,University of Genoa | Vignolo M.,CNR Institute of Neuroscience | Bovone G.,University of Genoa | And 5 more authors.
Superconductor Science and Technology | Year: 2013

A high-purity MgB4 phase has been synthesized and used as the precursor powder for the realization of in situ wires. Various final heat treatments, from 550 to 1100 ° C for 20 min each, have been carried out to convert the inner mixture to MgB2. Critical current densities up to 1.75 × 106 and 0.98 × 106 A cm-2 at 4.2 and 20 K, with 0.2 T, up to 0.76 × 105 A cm-2 at 4.2 K and 4 T, and up to 0.78 × 105 A cm-2 at 20 K and 2 T were measured. Critical temperatures up to 38.5 K were measured. These results suggest that this could be a good alternative to both ex situ and classical in situ routes. © 2013 IOP Publishing Ltd.

Morandi A.,University of Bologna | Brisigotti S.,Columbus Superconductors | Grasso G.,Columbus Superconductors | Marabotto R.,ASG Superconductors
IEEE Transactions on Applied Superconductivity | Year: 2013

The feasibility of a conduction-cooled MgB2 -based superconducting fault-current limiter with fast recovery is investigated. A real-scale device for a distribution network is considered. The dc resistive configuration is chosen in order to avoid ac losses and to allow conduction cooling. A high-heat-capacity cable is specifically developed in order to cope with the requirement of fast recovery. A short-length sample of the cable is manufactured in order to assess its feasibility. The detailed design of a prototype is also carried out, and the performance is numerically investigated. © 2002-2011 IEEE.

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